Fix PGXS support for building loadable modules on AIX.

Building a shlib on AIX requires use of the mkldexport.sh script, but we
failed to install that, preventing its use from non-source-tree contexts.
Also, Makefile.aix had the wrong idea about where to find the installed
copy of the postgres.imp symbol file used by AIX.

Per report from John Pierce.  Patch all the way back, since this has been
broken since the beginning of PGXS.

src/backend/Makefile

@@ -219,6 +219,7 @@ else
 endif
 ifeq ($(MAKE_EXPORTS), true)
 	$(INSTALL_DATA) $(POSTGRES_IMP) '$(DESTDIR)$(pkglibdir)/$(POSTGRES_IMP)'
+	$(INSTALL_PROGRAM) $(MKLDEXPORT) '$(DESTDIR)$(pgxsdir)/$(MKLDEXPORT_DIR)/mkldexport.sh'
 endif
 
 .PHONY: install-bin
@@ -237,6 +238,7 @@ endif
 endif
 ifeq ($(MAKE_EXPORTS), true)
 	$(MKDIR_P) '$(DESTDIR)$(pkglibdir)'
+	$(MKDIR_P) '$(DESTDIR)$(pgxsdir)/$(MKLDEXPORT_DIR)'
 endif
 
 
@@ -246,6 +248,7 @@ uninstall:
 	rm -f '$(DESTDIR)$(bindir)/postgres$(X)' '$(DESTDIR)$(bindir)/postmaster'
 ifeq ($(MAKE_EXPORTS), true)
 	rm -f '$(DESTDIR)$(pkglibdir)/$(POSTGRES_IMP)'
+	rm -f '$(DESTDIR)$(pgxsdir)/$(MKLDEXPORT_DIR)/mkldexport.sh'
 endif
 ifeq ($(PORTNAME), cygwin)
 ifeq ($(MAKE_DLL), true)

src/makefiles/Makefile.aix

@@ -27,12 +27,13 @@ endif
 POSTGRES_IMP= postgres.imp
 
 ifdef PGXS
-BE_DLLLIBS= -Wl,-bI:$(bindir)/postgres/$(POSTGRES_IMP)
+BE_DLLLIBS= -Wl,-bI:$(pkglibdir)/$(POSTGRES_IMP)
 else
 BE_DLLLIBS= -Wl,-bI:$(top_builddir)/src/backend/$(POSTGRES_IMP)
 endif
 
-MKLDEXPORT=$(top_srcdir)/src/backend/port/aix/mkldexport.sh
+MKLDEXPORT_DIR=src/backend/port/aix
+MKLDEXPORT=$(top_srcdir)/$(MKLDEXPORT_DIR)/mkldexport.sh
 
 %.exp: %.o
 	$(MKLDEXPORT) $^ >$@